1. Technical Field:
The present invention relates generally to computer system communications, and more specifically to a system for performing translations between communications procedures which use non-conforming interfaces.
2. Background Art:
Communications between two or more different computer systems usually involve the use of a serial communications link. Many different system and network architectures are in widespread use for performing inter-system serial communications. These architectures often use different, and incompatible, hardware, signaling techniques, data packet handling, and other features. Application programs executing on one system cannot, in general, communicate with applications executing on another system unless both systems support a common link architecture.
One reference model for communications standards is the Open Systems Interconnection (OSI) reference model, promulgated by the International Organization for Standardization. This model provides a seven layer structure. Ideally, each layer is independent, and communicates only with the layers directly above and below it. Actual implementations vary in the degree of success with which they make each layer independent.
The bottom layer of the OSI model is the physical layer, layer one. This layer defines the physical hardware and its interconnections. The second layer is the data link control layer, which performs error checking on transmitted packets and provides flow control.
The third layer is the network layer, which routes data through one or more networks and maintains network connections. Layer four is the transport layer, which ensures that all data packets are delivered correctly.
Layers five through seven comprise the session layer, presentation layer, and application layer, respectively. These higher levels provide functions needed by application programs to establish communications sessions between two systems and to manipulate transferred data.
Another well known communications architecture is Systems Network Architecture (SNA), which is available from IBM and widely supported. SNA has a structure which is similar to the OSI seven layer model. However, the layers, from an interface perspective, do not correspond. This means it is not possible for a SNA layer to communicate with an OSI layer.
It is not uncommon for a computer system to execute software implementing one communications architecture, but be required to connect to a network which uses a different communications architecture. In order to allow an application intended for communication using one architecture to function with a network based on another, it is possible to rewrite the software for the new architecture. This is a very time consuming and expensive task. In many installations, it is not possible or desirable to either rewrite software to allow it to function with a different communications architecture, or to change to a new software package intended for use with the other architecture and which may perform differently from the original package.
It is desirable, if possible, to have the communications architecture utilized on a network to be transparent to high level applications, and to allow such applications to function unmodified regardless of the underlying network type. It would be desirable to provide a system which allows existing applications to interface transparently with those which perform in accordance with a different communications architecture.